Ixii REPORT — 1856. 



These results, indeed, being merely negative, ought not to outweigh such 

 positive statements on the contrary side as come before us recommended by 

 respectable authority, such, for instance, as that respecting a Nelumbium 

 seed, which germinated after having been preserved in Sir Hans Sloane's 

 Herbarium for 150 years; still, however, they throw suspicion as to the 

 existence in seeds of that capacity of preserving their vitality almost indefi- 

 nitely} which alone would warrant us in calling to our aid this principle in 

 explaining the wide geographical range which certain species of plants affect. 



Let us then be content to appeal to those ingenious views which were first 

 put forth at one of our meetings by the late Professor Forbes, and which 

 have since been promulgated in a more detailed and systematic form by the 

 same distinguished naturalist. By the aid of the principles therein laid down, 

 he was enabled to trace the flora of Great Britain principally to four distinct 

 sources, owing to the geological connexion of these islands at one period or 

 other with Scandinavia, with Germany, with France, and with Spain ! And 

 it was by a similar assumption that Dr. Joseph Hooker explained the dis- 

 tribution of the same species throughout the islands of the Great Pacific, 

 and the contiguous continents, tracts which, as Darwiii had shown, were 

 formerly united. Nor is this mode of explanation limited to the case of the 

 above regions ; for in the ' Flora Indica,' which important work I regret to find 

 has been suspended after the appearance of the first volume. Dr. Hooker, in 

 conjunction with his fellow traveller. Dr. Thomson, has discussed the same 

 problem with regard to the whole of India, extending from AfTghanistan to 

 the Malayan peninsula. 



And amongst the many services rendered to the Natural Sciences by these 

 indefatigable botanists, one of the greatest 1 conceive to be, that they have 

 not only protested against that undue multiplication of species, which had 

 taken place by exalting minute points of diflPerence into grounds of radical 

 and primary distinction, but that they have also practically illustrated their 

 views with respect to the natural families which have been described by 

 them in the volume alluded to. They have thus contributed materially to 

 remove another difficulty which stood in the way of the adoption of the 

 theory of specific centres, — I mean the replacement of forms of vegetation in 

 adjoining countries by others, not identical, but only us it should seem allied ; 

 for it follows from the principles laid down by these authors, that such ap- 

 parently distinct species may after all have been only varieties, produced by 

 the operation of external causes acting upon the same species during long 

 periods of time. 



But if this be allowed, what limits, it may be asked, are we to assign to 

 the changes which a plant is capable of undergoing, and in what way can we 

 oppose the principle of the transmutation of species, which has of late ex- 

 cited so much attention, and the admission of which is considered to involve 

 such startling consequences? 



I must refer you to the writings of modern physiologists for a full discus- 

 sion of this question, and may appeal in particular to the lecture delivered 

 before this Association by Dr. Carpenter at our last meeting. All that I 

 shall venture to remark on the subject is, that had not Nature herself assigned 

 certain boundaries to the changes which plants are capable of undergoing, 

 there would seem no reason why any species at all should he restricted within 

 a definite area, since the unlimited power of adaptation to external conditions 

 which it would then possess might enable it to diffuse itself throughout the 

 world, as easily as it has done over that portion of space within which it is 

 actually circumscribed. 



